[WIP] [doc] performance/scalability revamp (#15723)

* [doc] performance/scalability revamp

* link the new docs

* no :

* mixed precision

* work on the first doc

* expand the main doc

* Trigger CI

* style

* revamp single GPU training section

* work on training performance

* remove files not used anymore or will be added later

* final touches

* fix rebase

* Add hardware section to toctree

* fix toctree again

* Apply suggestions from code review

Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

* remove `fast_tokenizers` entry that was copied in rebase

* add warning about DP vs DDP

* remove todo

* Apply suggestions from code review

Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

* fix missing closure of codeblock

* Update docs/source/en/perf_train_gpu_many.mdx

Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

* sync with #16860

* update toc

Co-authored-by: leandro <leandro.vonwerra@spoud.io>
Co-authored-by: Leandro von Werra <lvwerra@users.noreply.github.com>
Co-authored-by: Sylvain Gugger <35901082+sgugger@users.noreply.github.com>

docs/source/en/_toctree.yml

@@ -1,4 +1,4 @@
-- sections: 
+- sections:
   - local: index
     title: 🤗 Transformers
   - local: quicktour
@@ -60,11 +60,9 @@
   - local: serialization
     title: Export 🤗 Transformers models
   - local: performance
-    title: 'Performance and Scalability: How To Fit a Bigger Model and Train It Faster'
+    title: Performance and scalability
   - local: big_models
     title: Instantiating a big model
-  - local: parallelism
-    title: Model Parallelism
   - local: benchmarks
     title: Benchmarks
   - local: migration
@@ -83,6 +81,12 @@
     title: "How to add a model to 🤗 Transformers?"
   - local: add_new_pipeline
     title: "How to add a pipeline to 🤗 Transformers?"
+  - local: perf_train_gpu_one
+    title: Training on one GPU
+  - local: perf_train_gpu_many
+    title: Training on many GPUs
+  - local: perf_hardware
+    title: Custom hardware for training
   - local: testing
     title: Testing
   - local: pr_checks

docs/source/en/perf_hardware.mdx

@@ -0,0 +1,150 @@
+<!---
+Copyright 2022 The HuggingFace Team. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+-->
+
+
+# Custom hardware for training
+
+The hardware you use to run model training and inference can have a big effect on performance. For a deep dive into GPUs make sure to check out Tim Dettmer's excellent [blog post](https://timdettmers.com/2020/09/07/which-gpu-for-deep-learning/).
+
+Let's have a look at some practical advice for GPU setups.
+
+## GPU
+When you train bigger models you have essentially three options:
+- bigger GPUs
+- more GPUs
+- more CPU and NVMe (offloaded to by [DeepSpeed-Infinity](main_classes/deepspeed#nvme-support))
+
+Let's start at the case where you have a single GPU.
+
+### Power and Cooling
+
+If you bought an expensive high end GPU make sure you give it the correct power and sufficient cooling.
+
+**Power**:
+
+Some high end consumer GPU cards have 2 and sometimes 3 PCI-E 8-Pin power sockets. Make sure you have as many independent 12V PCI-E 8-Pin cables plugged into the card as there are sockets. Do not use the 2 splits at one end of the same cable (also known as pigtail cable). That is if you have 2 sockets on the GPU, you want 2 PCI-E 8-Pin cables going from your PSU to the card and not one that has 2 PCI-E 8-Pin connectors at the end! You won't get the full performance out of your card otherwise.
+
+Each PCI-E 8-Pin power cable needs to be plugged into a 12V rail on the PSU side and can supply up to 150W of power.
+
+Some other cards may use a PCI-E 12-Pin connectors, and these can deliver up to 500-600W of power.
+
+Low end cards may use 6-Pin connectors, which supply up to 75W of power.
+
+Additionally you want the high-end PSU that has stable voltage. Some lower quality ones may not give the card the stable voltage it needs to function at its peak.
+
+And of course the PSU needs to have enough unused Watts to power the card.
+
+**Cooling**:
+
+When a GPU gets overheated it will start throttling down and will not deliver full performance and it can even shutdown if it gets too hot.
+
+It's hard to tell the exact best temperature to strive for when a GPU is heavily loaded, but probably anything under +80C is good, but lower is better - perhaps 70-75C is an excellent range to be in. The throttling down is likely to start at around 84-90C. But other than throttling performance a prolonged very high temperature is likely to reduce the lifespan of a GPU.
+
+Next let's have a look at one of the most important aspects when having multiple GPUs: connectivity.
+
+### Multi-GPU Connectivity
+
+If you use multiple GPUs the way cards are inter-connected can have a huge impact on the total training time. If the GPUs are on the same physical node, you can run:
+
+```
+nvidia-smi topo -m
+```
+
+and it will tell you how the GPUs are inter-connected. On a machine with dual-GPU and which are connected with NVLink, you will most likely see something like:
+
+```
+        GPU0    GPU1    CPU Affinity    NUMA Affinity
+GPU0     X      NV2     0-23            N/A
+GPU1    NV2      X      0-23            N/A
+```
+
+on a different machine w/o NVLink we may see:
+```
+        GPU0    GPU1    CPU Affinity    NUMA Affinity
+GPU0     X      PHB     0-11            N/A
+GPU1    PHB      X      0-11            N/A
+```
+
+The report includes this legend:
+
+```
+  X    = Self
+  SYS  = Connection traversing PCIe as well as the SMP interconnect between NUMA nodes (e.g., QPI/UPI)
+  NODE = Connection traversing PCIe as well as the interconnect between PCIe Host Bridges within a NUMA node
+  PHB  = Connection traversing PCIe as well as a PCIe Host Bridge (typically the CPU)
+  PXB  = Connection traversing multiple PCIe bridges (without traversing the PCIe Host Bridge)
+  PIX  = Connection traversing at most a single PCIe bridge
+  NV#  = Connection traversing a bonded set of # NVLinks
+```
+
+So the first report `NV2` tells us the GPUs are interconnected with 2 NVLinks, and the second report `PHB` we have a typical consumer-level PCIe+Bridge setup.
+
+Check what type of connectivity you have on your setup. Some of these will make the communication between cards faster (e.g. NVLink), others slower (e.g. PHB).
+
+Depending on the type of scalability solution used, the connectivity speed could have a major or a minor impact. If the GPUs need to sync rarely, as in DDP, the impact of a slower connection will be less significant. If the GPUs need to send messages to each other often, as in ZeRO-DP, then faster connectivity becomes super important to achieve faster training.
+
+#### NVlink
+
+[NVLink](https://en.wikipedia.org/wiki/NVLink) is a wire-based serial multi-lane near-range communications link developed by Nvidia.
+
+Each new generation provides a faster bandwidth, e.g. here is a quote from [Nvidia Ampere GA102 GPU Architecture](https://www.nvidia.com/content/dam/en-zz/Solutions/geforce/ampere/pdf/NVIDIA-ampere-GA102-GPU-Architecture-Whitepaper-V1.pdf):
+
+> Third-Generation NVLink®
+> GA102 GPUs utilize NVIDIA’s third-generation NVLink interface, which includes four x4 links,
+> with each link providing 14.0625 GB/sec bandwidth in each direction between two GPUs. Four
+> links provide 56.25 GB/sec bandwidth in each direction, and 112.5 GB/sec total bandwidth
+> between two GPUs. Two RTX 3090 GPUs can be connected together for SLI using NVLink.
+> (Note that 3-Way and 4-Way SLI configurations are not supported.)
+
+So the higher `X` you get in the report of `NVX` in the output of `nvidia-smi topo -m` the better. The generation will depend on your GPU architecture.
+
+Let's compare the execution of a gpt2 language model training over a small sample of wikitext.
+
+The results are:
+
+
+| NVlink | Time |
+| -----  | ---: |
+| Y      | 101s |
+| N      | 131s |
+
+
+You can see that NVLink completes the training ~23% faster. In the second benchmark we use `NCCL_P2P_DISABLE=1` to tell the GPUs not to use NVLink.
+
+Here is the full benchmark code and outputs:
+
+```bash
+# DDP w/ NVLink
+
+rm -r /tmp/test-clm; CUDA_VISIBLE_DEVICES=0,1 python -m torch.distributed.launch \
+--nproc_per_node 2 examples/pytorch/language-modeling/run_clm.py --model_name_or_path gpt2 \
+--dataset_name wikitext --dataset_config_name wikitext-2-raw-v1 --do_train \
+--output_dir /tmp/test-clm --per_device_train_batch_size 4 --max_steps 200
+
+{'train_runtime': 101.9003, 'train_samples_per_second': 1.963, 'epoch': 0.69}
+
+# DDP w/o NVLink
+
+rm -r /tmp/test-clm; CUDA_VISIBLE_DEVICES=0,1 NCCL_P2P_DISABLE=1 python -m torch.distributed.launch \
+--nproc_per_node 2 examples/pytorch/language-modeling/run_clm.py --model_name_or_path gpt2 \
+--dataset_name wikitext --dataset_config_name wikitext-2-raw-v1 --do_train
+--output_dir /tmp/test-clm --per_device_train_batch_size 4 --max_steps 200
+
+{'train_runtime': 131.4367, 'train_samples_per_second': 1.522, 'epoch': 0.69}
+```
+
+Hardware: 2x TITAN RTX 24GB each + NVlink with 2 NVLinks (`NV2` in `nvidia-smi topo -m`)
+Software: `pytorch-1.8-to-be` + `cuda-11.0` / `transformers==4.3.0.dev0`